A document discusses alligation and mixtures, which is the ratio of quantities of items in a mixture. The ratio of the quantity of the first item to the second item is equal to the difference between the cost of the first item and the mean cost, divided by the difference between the cost of the second item and the mean cost. When ingredients of different costs are mixed together, the ratio of their quantities is inversely proportional to the differences between their individual costs and the mean cost of the mixture.